(Time sensitive question) I'm pretty sure I just got fired. How do I act?

I have a fundraising job and haven’t been making standards for a while now. I’m fully aware that things can’t continue how they are, and I leave for college in mid-August, so it’s not a huge deal.

I’ve been working where I work for five months, though, and have gotten close with my coworkers and bosses. Today I was out fundraising with a team of people including my boss, and got sick about an hour in. I tried to stick it out but half an hour later he came up to me and told me that I needed to go home. I asked if I could try to stick it out and he was like, “No. Go home. I’ll see you tomorrow morning, there are some other things I want to discuss with you as well.”

I sent him a text later asking if I was being fired tomorrow, because that was the impression I got. He responded “I’m not going to have this conversation over txt. But we do need to have a serious conversation tomorrow morning. I’ll see you then.”

This is my first job (I’m 18) and my bosses know that. I don’t know how to act. I’ve developed close personal friendships with both of them. I’m worried that I will cry when they tell me I’m fired. I also don’t know how formal to be with them—we’re usually super casual. What’s the etiquette for this kind of thing? The meeting is tomorrow morning first thing. Help!